Those three words, in that order, aren’t traditionally ones you’d apply — or want to apply — to a mystery. But rarely is the gulf between the details of the crime and the amount of fun you derive from witnessing them wider than it is in Murder for Two. Joe Kinosian and Kellen Blair’s frantic outing, which is playing at the McGinn-Cazale as part of the Second Stage Theatre Uptown series, bucks such familiarity with wanton, and not always unwanted, abandoned. As a result, most of what makes it notable has nothing to do with the particulars of its plot.

Whether this matters — or, in fact, should matter — is a question only you can answer, and doing so may prove more difficult than you may expect. Though I typically thrill much more to intricate narratives tightly tangled and explosively undone than I do rank expressions of theatrical possibility (along the lines of the relatively recent stage quasi-adaptation of The 39 Steps), I must admit that for the first three-quarters of this production, I couldn’t care less whether the characters played by scintillating stars Jeff Blumenkrantz and Brett Ryback ever actually got to the bottom of it. What’s more important is that I didn’t mind that I didn’t care.

Oh, I was vaguely aware that a killing had occurred. Some dialogue had been uttered to inform me that “Arthur Whitney, great American novelist” had been shot in the head, and that police officer-not-yet-detective Marcus Moscowicz (Ryback) was on hand to question the suspects (Blumenkrantz as, yes, all of them) and bring the perpetrator to justice. I had been (theoretically, at any rate) examining the evidence right alongside Marcus, and gaining the information I needed to make a determination of my own about guilt or innocence. But then something — anything — would happen, and librettist-composer Kinosian and librettist-lyricist Blair would yank me out of the story, and I never felt I was missing much.

This is because Blumenkrantz and Ryback are given essentially free rein over the stage (the suggestively Victorian basement–drawing room set is by Beowulf Boritt), and they’re worthy stewards of that trust. Both obviously tireless and athletic, they must surge through 90 minutes of not only dense (if daffy) characterizations, tinged with the romance and drama you’d expect of the genre, but also the requisite singing, dancing, and furnishing piano accompaniment. Kinosian, Blair, and director Scott Schwartz have ensured they never have a moment to rest, or even back down.

That’s the case from the very start of the evening, too, when the pair first appears engaged in a lengthy duel over control of the keys on the stage-center baby grand. But it quickly morphs into a different type of role playing as Blumenkrantz slides into his portrayal of Dahlia, Arthur’s husband, who reports his death and orders pizza at the same time. From there, it’s a narrow jump to following along Ryback’s sturdy-as-cedar, barely straight-man portrayal of Marcus as he takes over the case in attempt to win the badge he’s coveted since childhood, and the actor is more than intense enough to sell this least-crucial nuance.

More outwardly dazzling, of course, is Blumenkrantz, who flips between characters on milliseconds’ notice, rarely with more than a shift of position in his arm, leg, or facial muscles (though a pair of glasses does signal one of his more important subjects). But the show works because of two key elements: First, the contrast in looks and performing style between the two men, which at times makes you wonder if there really is a cast of thousands rather than a company of two; and that, when they’re closest to the center of the action, they don’t allow themselves in on the jokes.

The key word, and ultimately the key problem, is “center.” As long as Murder for Two sticks concretely to its premise and musicalizes, to whatever degree of silliness, the homicide investigation and the circumstances that immediately surround it, has no trouble scoring hits. Kinosian’s insinuatingly catchy tunes and Blair’s deft, at times Sondheimian, lyrics convey fun as readily as facts: Marcus’s “Protocol Says,” about the rules of police work, is a blisteringly fun opener; “He Needs a Partner,” a sweet ode sung by Whitney’s niece Steph who takes a strong liking to Marcus and his work; and “Process of Elimination” is a fast-paced parade through the final stages of deduction.

Alas, the myriad digressions are never as enjoyable. Sometimes they manifest themselves in small ways, with a grating, eye-rolling jokiness choked with myriad references to the art of creating the musical itself. (A pile of refuse that resembles the crime scene and a chair that stands in for a window are the prime beneficiaries.) Worse, Kinosian and Blair don’t always seem to care about making sense, even within their chosen strictures: The sudden appearance of a 12-member boys choir, which adds a quick-change “showstopper” but stops the proceedings as with a stun gun, and an endless, extraneous number in which Dahlia leaps across the fourth wall to fulfill her show-biz ambitions, do nothing to help the chaos cohere.

Good as their work otherwise is, Blumenkrantz, Ryback, and Schwartz cannot easily regain momentum after it’s halted in these ways, an issue that’s only exacerbated when the solution arrives and is revealed to be both unguessable and unfunny. That’s when this theatrical pick-me-up becomes a let-down, and Murder for Two all but commits suicide. Until then, however, you have no trouble reveling in the captivating human innovation that made it all possible, and that shouldn’t be discounted entirely — even if the writers’ inability to maintain the entertainment, when they’re so obviously talented and have such wonderful actor clay to work with, is the big mystery that never quite gets solved.